1. Field of the Invention
The invention relates to highly effective polarizers made from polyacetylene-containing polymer products with a matrix of pure polyvinyl alcohol (PVA), which have a high dichoric ratio Q.sub.E and at the same time a very high degree of polarization P. Polarizers of this type are used as film.
2. Descriotion of the Related Art
The preparation of polarizing films based on polyvinyl alcohol and iodine has been disclosed for example in DD 210,342. In this procedure, a polyvinyl alcohol film is subsequently coloured. In order to obtain any satisfactory results at all, complex processes of preparation and posttreatment are required. Moreover, as a rule only part of the film obtained in this manner is usable. The preparation of polarizing films of this type is limited in practice to iodine and additionally only to a few substances which are highly effective by virtue of dichroism.
The disadvantage with iodine-doped films is that the aggressive iodine migrates from the film; the disadvantage with films doped with dichroic substances is that they are coloured and can only be used for a narrow wavelength range.
Improved polarizers based on polyacetylene incorporated in polymer matrices have furthermore been disclosed in EP 249,019. Films obtained therefrom already have a high optical quality. For instance after the polymerization of acetylene in a solution of polyvinyl alcohol in DMF, a polarizing film is obtained which after 4-fold stretching has a light-polarizing efficiency of more than 90%.
However, for "high-tech" applications,these films which have been disclosed in the cited EP Application still do not have a sufficiently high dichroic ratio, which is defined as the quotient Q.sub.E of the extinction in the blocked position to the extinction in thetransmission position for plane-polarized light. The film mentioned in the exemplary embodiment of the cited EP Application is reddish-brown in colour.